bottle feeding with breastmilk

Asking for any advices how can i reteach my son to feed on a bottle...when he was 3 mos old he knew how to.. but now his turning 5 mos on March 4. He doesn't want to feed anymore ,i need to because ill be working very soon..i feel stressed because i keep on saving milk stash for future use but ending that my son doesn't want to consume it.help?